Thunberg planned to stay in the Americas to attend the United Nations COP25 climate summit in Santiago, Chile, in December, but the event was just moved to Madrid.

On Friday, Thunberg tweeted and asked for help crossing the Atlantic: „It turns out I’ve traveled half around the world, the wrong way,“ she said. „If anyone could help me find transport I would be so grateful.“

Because of air travel’s large carbon footprint, Greta Thunberg relies on trains and boats for transportation instead. But that’s put the Swedish 16-year-old in a bit of a bind.

Thunberg traveled from the UK to New York City on the Malizia II, a sailboat that runs on solar power (and wind, of course), in order to speak at the United Nations Climate Action Summit. Her plan was to stay in the Americas until the UN COP25 climate summit in early December.

But on Friday, the event got moved to Madrid because the Chilean capital is the throes of riots and protests.

Now Thunberg is looking for a low-emissions way to travel back across the Atlantic Ocean before COP25 commences on December 2.

„It turns out I’ve traveled half around the world, the wrong way,“ she tweeted on Friday, adding, „if anyone could help me find transport I would be so grateful.“

Could Thunberg travel home the same way she came?

To reach the US, Thunberg sailed with the crew of the Malizia II, a zero-emissions sailboat. Her father and a documentary filmmaker were on board too. The boat’s captain, Boris Herrmann, and fellow sailor Pierre Casiraghi volunteered to help them cross the Atlantic at no cost.

The 3,000-mile journey from Plymouth, England, to New York took 13 days, after which the crew of the Malizia II returned to Europe. Thunberg never planned to sail back on the Malizia II; her travel arrangements back to Sweden had always been up in the air.

Greta ThunbergKirsty Wigglesworth/AP

Even if Herrmann and Casiraghi did want to ferry Thunberg back across the Atlantic on the Malizia II, that might not be possible: The ship and its captain are in the mid-Atlantic, racing in the 114th Transat Jacques Vabre transatlantic sailboat race from Brazil to France.

To make matters more complicated, Thunberg is in Los Angeles, so it would take her at least three days to get back to the Atlantic’s shores by train.

Air travel’s heavy carbon footprint

A single round-trip flight between New York and California generates about 20% of the greenhouse gases your car emits in a year. Overall, the aviation sector accounts for 2% of annual global greenhouse-gas emissions. A 747 aircraft emits more than 21 pounds of carbon dioxide into the atmosphere per mile traveled.

Since arriving in North America, Thunberg has relied mostly on trains and buses to get to meetings and events.

She testified before the US Congress in September, chatted with Barack Obama, and gave a fiery, tearful speech to world leaders at the UN Climate Action Summit in New York.

Most recently, Thunberg has been traversing Canada, where she met with Canadian Prime Minister Justin Trudeau and joined climate strikes in Montreal and Vancouver, British Columbia, before returning to the US.

But since Chilean President Sebastian Pinera withdrew Santiago as the UN summit host, Thunberg no longer plans to travel farther south.

„I’m so sorry I’ll not be able to visit South and Central America this time, I was so looking forward to this. But this is of course not about me, my experiences or where I wish to travel. We’re in a climate and ecological emergency. I send my support to the people in Chile,“ Thunberg tweeted on Friday.